The continued drive for ever shrinking features in semiconductor manufacturing poses significant challenges for tool manufacturers and process developers alike. Requirements such as higher uniformity, tighter control of critical dimensions, reduced plasma damage, thinner layers, and shorter process times, combined with the introduction of new materials demand higher sophistication in the development of semiconductor processing tools. These requirements apply at the plasma chambers and go all the way down to the power delivery systems.
A human operator typically monitors multiple sensor outputs from a generator and a match network and adjusts numerous parameters in an imperfect and relatively slow attempt to maintain consistent power delivery to the plasma load. The operator may interact with an external controller that collects information from the various components of the system, displays this information for the operator, and transmits commands from the operator to the various components of the system. Although this configuration has worked in the past, it is increasingly apparent that it may not be adequate for current systems.
As an example, major advances in etch processes have been enabled by the introduction of a recent generation of RF power supplies with advanced capabilities, including generator frequency tuning while pulsing and multi-generator synchronized pulsing. Yet, even this cutting edge power delivery system is still being held back since the system components act independently and are therefore controlled independently. In particular, while the generator provides pulsed power with a tunable frequency, the match network has difficulty detecting, measuring, and responding to the pulsed signal and thus has difficulty taking advantage of the generator's capabilities. Operators tend to select an optimal variable capacitor position inside the match network and then run the process—a suboptimal solution for minimizing real time power reflection. So, while significant improvements have been made in plasma processing power supplies, they continue to be held back by the independent control of the generator and match network.
FIG. 1 illustrates a generator, match network, and plasma load well known to those of skill in the art. The generator 102 provides power to the plasma load 106 via the match network 104, where the match network 104 can alter an internal impedance such that as the impedance of the load 106 changes, an impedance seen by the generator 102 remains substantially constant (e.g., 50Ω). The match network 104 typically includes a sensor 116 that measures power incident upon the match network 104 and power reflected from the match network 104 back to the generator 102, and then uses these values to calculate an impedance of the plasma load 106. The generator 102 often includes a sensor 114 that measures power output of the generator 102. The sensors 114, 116 communicate their measurements to a user, sometimes via an external user interface 130. The user then instructs the match network 104 and/or the generator 102 to adjust in an attempt to tune the system.
In particular, the generator 102 can be instructed to produce a particular electrical characteristic (e.g., power or frequency) or a desired power delivered to the plasma load 106 can be selected and the generator 102 can tune to achieve that power. Similarly, the match network 104 can be instructed to operate at a particular impedance or can be instructed to tune in order to achieve a desired reflected power. In some cases, the generator 102 and the match network 104 can both be instructed to tune in order to meet desired power output characteristics.
The generator 102 sometimes includes a communications and logic board 112 that facilitates communication between the sensor 114, a radio frequency (RF) engine 113, and the user interface 130. The RF engine 113 can generate RF power and control the amplitude and waveform of the power generated by the generator 102. Similarly, the match network 104 sometimes includes a communications and logic board 122 that facilitates communications between the sensor 116, an impedance control system 115, and the user interface 130. The impedance control system 115 can control the impedance of the match network 104, for instance by having a motor drive board adjust variable capacitors of the match network 104.
This power delivery system 100 can be slow to adjust to changes in the plasma load 106 and dynamic power profiles from the generator 102 (power accuracy or consistency). For instance, there is a delay between the moment of measurement by either sensor 114, 116 and the moment when the measured values reach the user interface 130. There is also a delay when instructions are sent back to the generator 102 and the match network 104.
As for accuracy, the sensor 116 of the match network 104 only samples after a threshold current or voltage has been detected, and therefore is not sampling while the power is being compared to the threshold. A smaller sample size and the inability to sample from the start of pulsing leads to less accurate impedance measurements. Also, despite calibrating each sensor 114, 116, the sensors 114, 116 still have some level of error, and thus when used in combination, the net effect has an error roughly equivalent to the sum of the error of the individual sensors 114, 116. Finally, impedance measurements are most accurately taken when the frequency of power being measured is known. Since the sensor 116 of the match network 106 has to measure the frequency of power reaching the match network 104, and this measurement typically has some degree of error, the impedance calculated based on the sensor's 116 measurements typically also has some corresponding degree of error. As seen, speed and accuracy are limited in traditional systems resembling that of FIG. 1.
Quality may also be hampered in the art since the power delivery system 100's inaccuracy and slow speed can lead to inconsistent power delivery. In some cases, multiple generators feed power to a single plasma load via multiple match networks. Power quality is a particular issue in these cases since each generator and match network not only have to account for the plasma load, but also for the other generators, which are visible to each other. In other words, the impedance matching challenge is increased where multiple generators are involved, and thus power quality is further degraded when multiple generators are used.
While the system of FIG. 1 may have been adequate in the past, it may not be adequate to provide quickly adjusting, accurate, and consistent power to nonlinear, dynamic plasma loads characteristic of new processes with more stringent requirements of accuracy and stability and short processing steps.